V O L U M E 20, N O . 11, N O V E M B E R 1 9 4 8 LITERATURE CITED
(1) Baeyer, A., and Villiger, V., Ber., 34,854 (1901). D'Ans, J., and Frey, W., Ibid., 45, 1845 (1912). D'Ans, J., and Frey, W., Z.anorg. Chem., 84,145 (1913). D'Ans, J., and Kneip, A.,Ber., 48,1136 (1915). Findley, T., Swern, D., and Scanlan, J., J . Am. Chem. sot., 67,
(2) (3) (4) (5)
412 (1945). (6) Furman, N. H., and Wallace, J. H., Ibid.,51, 1449 (1929).
1063 (7) Greenspan, F. P., Ind. Eng. Chem., 39,847 (1947). (8) Greenspan, F. P., J . Am. Chem. Soc., 68, 907 (1946).
(9) Swern, D., private communication. (10) Swern, D., Billen, G., Findley, T., and Scanlan, J., J. Am. Chem. Soc., 67, 1786 (1945). RECEIVEDM a y 25, 1948. Presented before t h e Division of Analytical a n d Micro Chemistry a t the 113th meeting of t h e AMERICAN CHEMICAL SOCIETY, Chicago, Ill.
Determination of Small Amounts of Benzene in Ethyl Alcohol D. L. KOLBA, L. R. KANGAS, AND W. W. BECKER Hercules Experiment Station, Hercules Powder Company, Wilmington 99, Del. Small amounts of benzene (0.05 to 1.0% by volume) in ethyl alcohol may be determined by taking advantage of the difference in refractive indices of benzene (1.5014) and hexane (1.3754). The sample of alcohol is diluted with water and partially distilled; the alcohol fraction containing the benzene azeotrope is collected and extracted with hexane. The refractiveindex of the hexane-benzene mixture is measured, and its benzene concentration read from a graph. The difference in the specific gravities of benzene (0.879) and hexane (0.660) provides a second method of measuring the benzene in the hexane extract.
I
K T H E manufacture of solvent types of smokeless powder a t the ordnance plants during World War 11, large quantities of 2B ethyl alcohol, which contains 0.5y0benzene by volume, were used. After its recovery in plant stills, the alcohol contained varying amounts of benzene (0.05 to l.0701, which had to be accurately determined. Some lots rontained up to 1% ether. The methods of D o h ( 4 ) and Baernstein (3) could not be applied directly to the determination of benzene in alcohol. The generally accepted method has been that of Babington and Tingle ( 2 ) . However, when their method was applied to known alcohol-benzene mixtures, high results were obtained, the error varying with the amount of benzene present. It was found that use could be made of the dilution-distillation step of their procedure, in which the benzene comes over in the azeotropic mixture boiling a t 64.9" C. (1). The distillate was extracted with hexane, the refractive index of the hexane-benzene mixture was measured, and the benzene content was then read from a graph prepared by using known mixtures. I t was found also that the measurement of the specific gravity of the hexane-benzene mixture could be used to determine the concentration of the latter. BABINGTON AND TINGLE METHOD
In the method of Babington and Tingle ( 2 ) a diluted sample of the alcohol is distilled, and the first 20-ml. fraction is collected and treated with potassium dichromate This reaction mixture is then extracted with petroleum ether, and the increase in volume of the latter is a measure of the benzene present. This method was applied to several known alcohol-benzene mixtures. The results in Table I show not only that this procedure gives high results, but that the magnitude of the error varies with the amount of benzene present-for example, when the method was applied to pure 190-proof grain alcohol, an apparent benzene content of 0.20 to 0.25% was found. No significant improvement resulted when the method was modified by measuring the decrease in volume of the aqueous layer after extraction. If the chemistry of the method is considered critically, it becomes evident that only a little of the alcohol is oxidized by the dichromate. Only 0.45 gram of potassium dichromate is added, whereas 55.5 grams would be required to oxidize 20
ml. of 80% alcohol to acetic acid. It would seem that the additiog of less than 1% of the theoretical amount of potassium dichromate serves no useful purpose. In several experiments the potassium dichromate oxidation step was omitted. The alcohol was extracted directly with petroleum ether and the latter was extracted with water. The use of a higher boiling hydrocarbon, hexane, was also tested. While fair results were obtained on 2B ethyl alcohol alone, they were too high when the alcohol contained added ether. The measurement of the decrease or increase in volume, therefore, did not appear feasible. REFRACTIVE INDEX METHOD
In the evaluation of the refractive index procedure, known hexane-benzene solutions were prepared and their refractive indices were measured. The plotted values were found t o lie on a straight line. However, when known amounts of benzene were added to 20-ml. pxtion3 of 83% (by w2ight) alcohol and these mixtures were extracted with 10-ml. portions of hexane, the refractive indices of the latter were lower than the calculated values. This was presumably due to dissolved alcohol, which has a refractive index of 1.3624. Accordingly, 25-ml. portions of saturated sodium chloride solution were added to 20-ml. portions of 80% alcohol containing benzene, and these mixtures were extracted with 10-ml. portions of hexane. The refractive indices of the latter agreed closely with the calculated values. A typical refractive index-benzene concentration graph is shown in Figure 1. The alcohol recovered from some plant operations may contain
Table I. Determination of Benzene in Known AlcoholBenzene Solutions by Babington and Tingle Method Benzene Added t o !OO Ml. of Grain Alcohol MI. 0.00 0.20
0.50 0.80 1.oo
Benzene Found Increase in volume of Decrease in volume petroleum ether layer of aqueous layer MI. MI. 0.20 0.40 0.65 0.92 1.15
0.25
...
0.68 0.95
...
ANALYTICAL CHEMISTRY
1064 v 1.3939-
x
W
0
z
z/ ~1.3919-
'
0
tl
'
E
O
W
/
U
>
5
Transfer the distillate to a 125-ml. Squibb separatory funnel and add 25 ml. of saturated sodium chloride solution, using the same graduate. Add 10.0 ml. of hexane from a buret, stopper the funnel, and shake vigorously for 30 seconds. Bfter the two layers have separated, discard the aqueous layer. If the presence of ether is suspected, wash the hexane first with three 25-1111. portions of water and finally with 25 ml. of saturated salt solution. Measure the refractive index of the hexane a t 20" C. If the determination is made a t a higher temperature, add 0.00044 per 1 C. From the corrected value, subtract the refractive index of the hexane itself. From the increase in refractive index, read the concentration of benzene in the sample from the graph. In preparing the graph, dilute grain alcohol to 80% by weight. To 20-ml. portions, add known amounts of benzene, preferably from a microburet, followed by 25-ml. portions of saturated salt solution. Extract with 10-ml. portions of hexane and measure the refractive indices.
0 .oo80
W
W
t.y99-
o,mo: z 0.0060
O
W
c
U W
U
1.3879-
I.3859
2
-
0 .m20
I ML. BENZENE
AOOED
Figure 1. Increase in Refractive Index of Hexane after to Which Varying Extraction Of 2o 'I1* Of 80'% Amounts of Benzene Have Been Added
Analysis of Known Mixtures. Several known solutions of 190proof grain alcohol containing benzene and ether were analyzed by the foregoing procedure. Table I11 shows that benzene may be determined with an accuracy of 0.02% of the volume of the sample.
Table 11. -4queous Extraction of Hexane-Benzene-Ether Solutions Followed by Measurement of Benzene Content
-,".
x--
10.0
0.50
0.0
10.0
0.50
0.5
10.0
0.50
1.0
t:% Re:lfg:ve Benzene a t 20' C. Found
Water
1.3899 1,3899 1,3900 1,3893 1,3898 1.3897 1.3896
0.50 0.50 0.51 0.45 0.49 0.48
0.47
. ..
Because all laboratories are not eauiuued with refractometers. the feasibility of taking advantage of the considerable difference
-I "L
Extraccomposition of Solutions Hexane Benzene Ether
DISTILLATION-SPECIFIC GRAVITY METHOD
Error
+0.01 -0.05 -0.01 -0.02 -0.03
0.0080
0.6741
0.0 0.0
2
0.6721
>
t
z small amounts of ether.
Because the refractive index of ether
results (1.3497)will is lower be obtained than that unlessof the hexane ether(1.3754), is removed lowfrom benzene the hexane layer. ' On addition of known amounts of ether (0.5 to 1.0 ml.) t o 20 ml. of 8070 alcohol and extraction with 10 ml. of hexane, the ether was found to dissolve largely in the hexane Layer. This layer was washed with successive portions of water to remove the ether, a final washing made with salt solution, and the refractive index was measured. The data in Table 11 show that three extractions are adequate to remove the ether. Apparatus and Reagents. Distilling flask, 500-ml. The side arm should be suitably bent and connected to a 30-cm. (12-inch) vertical Liebig condenser. Refractometer, Abbe type. %-Hexane, technical grade; refractive index a t 20" C., 1.3754 to 1.3870; Jree of water-soluble impurities (determined by shaking with water and observing no change in volume). A new graph should be constructed with each new lot of hexane. Alcohol, grain, 190-proof (9570). Benzene, thiophene-free. The alcohol and benzene are used in preparing a graph based on known mixtures, similar to Figure 1. Procedure. The following procedure is applicable to 95T0 alcohol containing 0.05 to l.0y0 benzene and up to l.O$TO ethyl ether. By means of a graduate, measure 100 ml. of the alcohol to be tested into a 500-ml. distilling flask and add 200 ml. of water along with a few particles of Carborundum. Connect the flask to the condenser and distill, collecting the distillate in a 25-ml. cylinder immersed in ice water. Distill 20 ml. a t the rate of 1.0 to 1.5 ml. per minute. The distillate consists of SOTo alcohol ( b r weight) and contains all the benzene.
Table 111.
2
~oo040
06701
2
/O'
o
6681~
2
0
0
0
0 om00
0 6661
0
11-11.
100 100 100 100
0.0
100
Table IV.
0
/
~
I
02
0 4
08
06
1.0
ADDED
Determination of Benzene in Known Alcohol-Benzene Mixtures by Distillation-Refractive Index Method
MZ.
100
~
ML BENZENE
Composition of Solutions 'Alcohol Benzene Ether
100 100 100
0
Figure 2. Increase in Specific Gravity of Hexane after Extraction of 20 ~ 1 of. 80% Alcohol to Which Varying Amounts of Benzene Have Been Added
No. of Water Washings of
100 100
2
E % : t
of Distillate
0.75 0.50 0.50
a t 20° C.
Increase in Refractive Index
MZ.
n
n
0.05 0.10 0.25 0.50 0.76 1 .oo 0.25
Refractive Index of
0 0.5 0.5 0.5 1.0
6
1.3869 1.3861 1.3864 1.3878 1.3899 1.3917 1,3937 1,3877 1.3917 1 ,3900 1.3897
0.0002 0,0005 0.0019 0.0040 0.0058 0.0078 0,0018 0.0058 0.0041 0.0038
Benzene Found in Distillate
Error
M1.
M1.
0.05 0.10 0.26 0.50 0.73
+0.01
1.01
+0.01
0.25 0.73 0.51 0.48
+o. 01
...
...
0.00 0.00
0.00 -0.02
0.00 -0.02 -0.02
Determination of Benzene in Known Benzene-Alcohol Mixtures by Distillation-SDecific Gravitv Nethod No. of Water
Composition of S O l u t i o n g Alcohol Benzene Ether M1. Ml. MI. 100 0.00 0.0 100 0.30 0.0 0.0 100 0.45 1 ,? 100 0.45 0.0 100 0.50 0.5 100 1.00
Washings of Hexane Extract of Distillate
SP. Gr. of Hexane Extract of Distillate a t 2Oo/2O0C.
0 2 2 3 3 3
0,6661 0.6681 0.6691 0.6693 0,6696 0,6732
Increase in Sp. Gr. 0.0020 0.0030 0,0032 0.0035 0.0071
Benzene Found in Distillate -111.
Errol
0.30 0.44 0.47 0.51
0.00 -0.01 +0.02 $0.01 -0.01
...
0.99
MI.
...
1065
V O L U M E 20, NO. 11, N O V E M B E R 1 9 4 8 in the specific gravity of benzene (0.879) and hexane (0.660) was investigated. In order to measure the specific gravity by means of a Westphal balance, a minimum of 25 ml. of liquid is necessary.
Mixtures of 20 ml. of 80% alcohol (containing added benzene) and 25 ml. of saturated salt solution were extracted with 25-ml. portions of hexane, and the specific gravities of the latter were measured. The results obtained were slightly lower than the calculated values. The hexane extract was therefore first washed with two 25-ml. portions of water to remove dissolved alcohol, followed by a final wash with 25 ml. of saturated salt solution. The specific gravities of the extracted hexane were then found to agree closely with the calculated ones. A typical specific gravity-concentration Figure 2.
graph is shown in
Apparatus and Reagents. The apparatus and reagents required for this determination are the same as listed under the refractive index method, except that a Westphal-type balance is substituted for the refractometer. I n the authors' work, a Christian Becker Chain-0-matic specific gravity balance, Catalog KO.110, range zero to 2.000, standardized a t 20' C., was used. Procedure. Dilute the alcohol sample, distill as described under the refractive index method, and transfer the distillate to a 250-ml. Squibb separatory funnel. Add 25 ml. of saturated salt solution and 25.0 ml. of hexane, stopper the funnel, and shake vigorouslv for 30 seconds. After the two layers have separated, discard the aqueous layer. Wash the hexane with two 50-ml. portions of water (three if ether is suspected t o be present) and finally with 25 ml. of saturated salt solution. Transfer the hexane layer to a 25-ml. cylinder and determine its specific gravity a t 20°/20" C. If the determination is made a t a higher temperature, add 0.00086 per 1' C. From the corrected reading subtract the specific gravity of the hexane itself a t 20"/20" C., and from
the graph, prepared by applying the foregoing procedure to known mixtures, read the concentration of benzene in the sample. Analysis of Known Mixtures. The foregoing method, including the distillation step, was used to analyze several known mixtures of alcohol-benzene, some of which contained added ether (Table IV). The results possess the same accuracy as those found by the distillation-refractive index procedure. SUMMARY
The method of Babington and Tingle for benzene in alcohol gave results which were considerably too high. Furthermore, it was shown that the chemistry of their method is unsound. Two methods for the determination of benzene in alcohol, accurate within 0.02% of the volume of the sample, have been developed. One depends on the difference between the refractive indices of benzene and hexane, and the other depends on the difference between their specific gravities. A small amount of ether does not interfere. ACKNOWLEDGMENT
The authors wish to thank E. B. Spaulding and Floyd Diephuis, formerly of the Badger Ordnance Works, now a t the Parlin, S . J., plant and Experiment Station, respectively, for helpful suggestions regarding the method. LITERATURE CITED
(1) Atkins, W. R. G., Nature, 151, 449 (1943). (2) Babington, F. IF'., and Tingle, Alfred, J . Ind. Eng. Chern., 11, 556 (1919). (3) Baernstein, H. D., IXD. ENG.GREY., ANAL.ED.,15, 251 (1943). (4) Dolin. B. H., Ibid., 15, 242 (1943).
RECEIVED February 9, 1947.
Determination of Small Amounts of Benzene in Ethyl Ether S. L. R.IIREL1, D. L. KOUBA, AND W. W. BECKER Hercules Experiment Station, Hercules Powder Company, W'ilmington 99, Del. Small amounts of benzene (0.2 to 1.2'70) in ether may be determined within 0.05% of the volume of the sample by making use of the difference in the specific gravities of benzene (0.879) and ether (0.720). The benzene is concentrated in about one third of the ether by distillation, and the specific gravity of the residue is determined.
I
S CONSECTIOS with the operation of ordnance plant3
Advantage was taken of the considerable difference between the specific gravit,ies of benzene (0.879) and ether (0.720). The method consists in distilling off about tn-o thirds of the ether to concentrate the benzene, measuring the specific gravity of the residue, and reading its benzene content from a graph prepared by using known mixtures. The results, expressed as per cent benzene, are acAnalysis of Known Benzene-Ether Solutions and Plant-Rectified Ether curate xithin 0.05 unit. Benzene in Benzene Difference The general principle of this Benzene Specific Distillation Found in between Residue Sample, Added, Gravity Volume of .$mounts procedure was developed to Volume of Residue Residue after (Read from Volume Present Basis a t 2Oo/2O0 C. Distillation B , Fig. 1) Basis a n d Found determine small amounts of 9% M1. % % % benzene in alcohol (1).
manufacturing solvent types of smokeless powder during World K a r 11, a method was desired for determining small amounts of benzene in ethyl ether, which had been manufactured from 2B ethyl alcohol containing 0.5% benzene.
Table I.
Sample la
2a 3 3 4 4 4 6
a b
0.40 0.60
0:sia 01666
0.86b
0.7207 0.7218 0.7202 0.7220 0.7212 0.7223 0.7230 0.7211 0,7222
5 0:63b Known benzene-ether solution. Includes original benzene determined previously.
44.5 44.5 47.0 47.0 43.5 41.0 46.5 41.5 42.5
1.31 1.96 1.00 2.08 1.60 2.27 2.70 1.54 2.21.
0.39 0.58 0.31 0.65 0.46 0.62 0.84 0.43 0.63
-0.01 -0.02
+0:04 ,.. -0.04 -0.02
...
EXPERIMENTAL
In evaluating the specific gravity method, small amounts
0.00 1 Present address, F. 0. Pierce Company, Long Island City,
K. Y.
